Wide range pressure controlled spark gap

ABSTRACT

An adjustable spark gap device in which both the electrode spacing and the gas pressure are adjustable to provide a wide range of breakdown voltages. The electrodes are mounted so that the spacing and the gas pressure are simultaneously adjusted by changing only the gas pressure, so that only a single control is required for adjustment over a wide voltage range.

United States Patent 1191 Spencer Feb. 18, 1975 WIDE RANGE PRESSURE CONTROLLED 2,441,284 5/1948 Parrish 313/146 x SPARK GAP 3,229,145 1/1966 Jensen 313/146 3,517,248 6/1970 Eckel 313/214 X [75] Inventor: Willard E. Spencer, Renton, Wash.

[73] Assignee: The Boeing Company, Seattle, Primary Examinerlames Lawrence w Assistant Examiner-Wm. H. Punter Attorne A em, or FirmBrown, Murra Flick & [22 "F1led: May 14, 1973 Peckharyn g y [21] Appl. No; 360,304

[57] ABSTRACT 52 us. 01. .l 313/146, 313/184 An adjustable Spark p device in which both the elec- 51] 1111. C1. 1101; 1/88 Spacing and the gas pressure are adjustable to [58] Field of Search 313/146-148, Provide a wide range of breakdown voltages- The elec- 313/183 1g4 2 trodes are mounted so that the spacing and the gas 3 pressure are simultaneously adjusted by changing only [56] References Cited the gas pressure, so that only a single control is re- UNITED STATES PATENTS quired for adjustment over a wide voltage range.

706,74l 8/190; Fessendenm 313/184 x 9 Claims, 2 Drawing Figures IIIIIIIIIII'III WIDE RANGE PRESSURE CONTROLLED SPARK GAP BACKGROUND OF THE INVENTION This invention relates generally to spark gap devices, and more particularly to an adjustable spark gap which can be controlled to provide a wide range of breakdown voltages.

Adjustable spark gaps are useful in many high voltage devices for purposes such as switching high voltage pulses in test equipment, and for use in such devices as pulsers, Marx generators and high voltage protective devices. In these devices the gap functions as an on-off switch which becomes conductive when the voltage across it exceeds a preset value. These spark gaps must therefore usually be adjustable to set the breakdown voltage at the desired value. The breakdown voltage can be varied by changing the electrode spacing of the gap and by changing the pressure of the gas in the gap and both types of adjustment are known. Gaps in which both the spacing and the pressure can be adjusted are also known, but such gaps involve separate adjustment of two independent parameters which is time consuming and often makes it difficult to set the voltage with the desired degree of accuracy and reproducibility. Mechanical linkages are often used for adjusting the gap spacing and this introduces a safety problem on high voltage equipment, so that the adjustment must be controlled by complicated remote means, or the equipment must be completely deenergized, or isolated from the high voltage, each time an adjustment is made which is very time consuming.

SUMMARY OF THE INVENTION The present invention provides an adjustable spark gap'device in which both the spacing between electrodes and the gas pressure are adjustable, to obtain a very wide range of adjustment, but in which adjustmentsare quickly and easily made by means of only one control and without any safety problem.

These results are accomplished by mounting at least one of the electrodes on a bellows which contains a compression spring and in which the interior pressure is maintained substantially constant, as by venting the bellows to atmosphere. When the gas pressure in the gapis increased, above the pressure in the bellows, the bellows is compressed and the gap spacing increases. Thus, when the gas pressure is changed, the gap spacing also changes, and both spacing and pressure are simultaneously adjusted by changing only the gas pressure. A wide range of breakdown voltage can thus be provided with a simple, easily adjusted control and with no safety problem.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a sectional view of an illustrative embodiment of the present invention; and

FIG. 2 shows typical operating characteristics of a gap embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the adjustable gap device of FIG. 1 an upper electrode 2 and a lower electrode 4 are spaced apart form-.

ing a spark gap 3 therebetween. The lower electrode 4 is fixed in position, as by a clamping nut 6, on a lower end cap 8, while the upper electrode 2 is supported on anv upper end cap 10. The end caps 8 and 10 may be made of any suitable material and are clamped at each end of an insulating envelope 12 which is sealed by 0- rings 14. Insulating tension rods 16 and nuts 18 clamp the end caps 8 and 10 against the envelope 12 to form a gas-tight seal.

The upper end cap 10 carries a conducting bushing 20 through which electrical contact may be made to the upper electrode 2. An internally threaded conducting sleeve 22 is threaded on the bushing 20 and clamps it on the end cap, the joint being sealed by anO-ring 24. A bellows 26 is attached to the lower end of the sleeve 22 and sealed thereto, as by soldering or in any other suitable manner, and the upper electrode 2 is attached to the bellows, the lower end of the bellows being closed and sealed. A compression spring 28 is contained within the bellows 26 bearing against the lower end of the bellows, and an adjusting nut 30 is threaded into the sleeve 22 and engages the upper end of the spring 28 to compress it. A vent 32 preferably extends through the nut 30 to vent the interior of the bellows to atmosphere through the bushing 20. A port 34 is provided in the upper end cap 10 with a suitable fitting 36, preferably of insulating material, for connection of a hose 38 through which an inhibiting or inert gas is introduced into the sealed gap enclosure. Suitable means (not shown) are provided in the gas supply for controlling or adjusting the gas pressure in the gap enclosure.

The lower electrode 4 is preferably mounted on the lower end cap 8 as previously described, although it might be movably mounted in the same manner as the upper electrode if desired. In the preferred embodiment'ofthe invention illustrated, a triggering electrode is also provided. Suchelectrodes are used for precise control of voltage or firing time of the gap, and are often used when several gaps must fire simultaneously to discharge multiple-section equipment. As shown in FIG. 1, a trigger electrode 40 extends through the lower electrode 4 to its upper surface and is insulated from the lower electrode by an insulating sleeve 42. The main gap 3 can then be fired by applying a high voltage pulse to the trigger electrode 40 which causes a preliminary discharge between the trigger electrode and the lower electrode 4. The preliminary discharge triggers the discharge in the main gap. Other types of triggering electrodes are also known and may be utilized. For many purposes, it is not necessary to use a triggering electrode and it may, of course, be omitted.

When a high voltage is impressed across the electrodes 2 and 4, sparkover occurs if the breakdown voltage of the gap is exceeded. The breakdown voltage of the spark gap is very nearly a direct function of the absolute pressure of the gas in the sealed enclosure. The breakdown voltage is also very nearly a direct function of the distance separating the electrodes 2 and 4. The range of adjustment of the breakdown voltage can therefore be increased by providing for adjustment of both the gap spacing and the gas pressure. Such adjustment, however, has heretofore required two separate adjusting means and has often involved complicated mechanical linkages, or unacceptable risks due to the high voltages, or both, as discussed above.

In accordance with the present invention, the gap spacing and the gas pressure are simultaneously adjusted by a single control and without requiring any mechanicallinkages or involving any safety hazards. This is accomplished by means of the mounting of the upper electrode on the bellows 26. The bellows is vented to atmosphere or other fixed pressure through the port 32, or may be sealed to maintain substantially constant internal pressure. As the pressure of the gas is increased above the pressure in the bellows 26, the bellows is compressed thereby causing the electrode 2 to move and increase the gap spacing. The spring 28 resiliently opposes this movement and the spring constant is chosen to give the desired change of gap space with pressure. An initial zero adjustment is preferably made by means of the adjusting nut 30 which is screwed in until the two electrodes just touch with atmospheric pressure in the gapor, more generally, with the same pressure in the bellows and in the gap. As the gas pressure is then increased, the gap spacing will vary with the gas pressure, and the breakdown voltage will vary with the gap spacing and the gas pressure. Thus, the breakdown voltage is varied by changing only the gas pressure and a single control provides the desired adjustment over a wide range of voltages.

The curves of FIG. 2 illustrate the improved characteristics of the new gap. Curve A shows the relation of gas pressure to breakdown voltage in a typical gap of the structure of FIG. 1 when the gas used is nitrogen and curve B shows the relation when the gap contains sulphur hexafluoride. It will be seen that a very wide range of adjustment is obtainable, extending from essentially zero to 150 kilovolts with sulphur hexafluoride.

While the present invention has been described with a degree of particularity for the purposes of illustration, it is to be understood that all modifications and embodiments within the spirit and scope of the present invention are herein meant to be included. I claim as my invention:

1. An adjustable spark gap device for continuous adjustment over a wide range of breakdown voltages comprising a fixed electrode and a movable electrode spaced apart to form a spark gap therebetween, a gastight enclosure for said electrodes, a compressible bellows device in said enclosure, said movable electrode being mounted on said bellows for movement therewith toward and away from the fixed electrode, means for maintaining substantially constant pressure within the bellows device, and means for admitting gas into the enclosure at a controlled and adjustable pressure differing from the pressure within the bellows to simultaneously adjust said gas pressure and the spacing between said electrodes.

2. A spark gap device as defined in claim 1 in which the bellows is open to atmospheric pressure.

3. A spark gap device as defined in claim 1 including spring means opposing compression of the bellows.

4. A spark gap device as defined in claim 3 in which the spring means is a compression spring disposed within the bellows.

5. A spark gap device as defined in claim 3 in which the bellows is open to atmospheric pressure.

6. A spark gap device as defined in claim 1 in which one of said electrodes is adjustably mounted in the enclosure.

7. An adjustable spark gap device for continuous adjustment over a wide range of breakdown voltages comprising a sealed, gas-tightenclosure, a pair of electrodes in said enclosure disposed to form aspark gap therebetween, at least one of said electrodes being mounted for movement toward and away from the other electrode, a compressible bellows device in the enclosure, said one electrode being mounted on said bellows, means for maintaining substantially constant pressure within the bellows device, the bellows device including means for resiliently opposing compression of the bellows, and means for admitting gas into the enclosure at a controlled and adjustable pressure to simultaneously adjust said gas pressure and the spacing between said electrodes.

8. A spark gap device as defined in claim 7 in which the bellows device includes a compression spring.

9. A spark gap device as defined in claim 7 in which the bellows device is vented to atmospheric pressure. 

2. A spark gap device as defined in claim 1 in which the bellows is open to atmospheric pressure.
 3. A spark gap device as defined in claim 1 including spring means opposing compression of the bellows.
 4. A spark gap device as defined in claim 3 in which the spring means is a compression spring disposed within the bellows.
 5. A spark gap device as defined in claim 3 in which the bellows is open to atmospheric pressure.
 6. A spark gap device as defined in claim 1 in which one of said electrodes is adjustably mounted in the enclosure.
 7. An adjustable spark gap device for continuous adjustment over a wide range of breakdown voltages comprising a sealed, gas-tight enclosure, a pair of electrodes in said enclosure disposed to form a spark gap therebetween, at least one of said electrodes being mounted for movement toward and away from the other electrode, a compressible bellows device in the enclosure, said one electrode being mounted on said bellows, means for maintaining substantially constant pressure within the bellows device, the bellows device including means for resiliently opposing compression of the bellows, and means for admitting gas into the enclosure at a controlled and adjustable pressure to simultaneously adjust said gas pressure and the spacing between said electrodes.
 8. A spark gap device as defined in claim 7 in which the bellows device includes a compression spring.
 9. A spark gap device as defined in claim 7 in which the bellows device is vented to atmospheric pressure. 